1. Field of the Invention
This document relates to a plasma display panel, in particular to a plasma display apparatus and driving method of same, wherein the bightness of sustain light generated by a sustain pulse by performing floating either a scan electrode or a sustain electrode during a sustain period, thereby increasing the driving efficiency of the plasma display apparatus.
2. Description of the Background Art
Generally, in a plasma display panel, barrier ribs formed between a front substrate and a rear substrate form unit or discharge cells. Each of the cells is filled with a main discharge gas, such as neon (Ne), helium (He), or a mixture of Ne and He, and an inert gas containing a small amount of xenon. When it is discharged by a high frequency voltage, the inert gas generates vacuum ultraviolet rays, which thereby cause phosphors formed between the barrier ribs to emit light, thus displaying an image. Because the plasma display panel can be made with a thin and/or slim form, it has attracted attention as a next-generation display device.
FIG. 1 is a perspective view illustrating the configuration of a related art plasma display panel.
As shown in FIG. 1, in the plasma display panel, a front panel 100 and a rear panel 110 are coupled in parallel with each other depart from a predetermined distance. In the front panel 100, a plurality of sustain electrode pairs formed by a pair of a scan electrode 102 and a sustain electrode 103 are arranged on a front substrate 101. In the rear panel 110, a plurality of address electrodes 113 are arranged to intersect the plurality of sustain electrode pairs on a rear substrate 111.
The front panel 100 comprises pairs of the scan electrode 102 and the sustain electrode 103. The scan electrode 102 and the sustain electrode 103 perform reciprocal discharges in a discharge cell and sustain light emitting of the cell. The scan electrode 102 and the sustain electrode 103 are provided with a transparent electrode (a) made of a transparent ITO material and a bus electrode (b) made of a metallic material. The scan electrode 102 and the sustain electrode 103 are covered with one or more upper dielectric layers 104 to limit discharge current and provide insulation among the electrode pairs. A protection layer 105 having magnesium oxide (MgO) deposited thereon in order to facilitate a discharge condition is formed on top of the upper dielectric layer 104.
In the rear panel 110, barrier ribs 112 are arranged in the form of a stripe pattern (or a well type), while a plurality of discharge spaces or discharge cells are formed in parallel. Furthermore, a plurality of address electrodes 113 for performing an address discharge to generate vacuum ultraviolet rays are disposed parallel to the barrier ribs 112. The top surface of the rear panel 110 is coated with R, G, and B phosphors 114 for emitting visible rays for an image display when an address discharge is carried out. A lower dielectric layer 115 is formed between the address electrodes 113 and the phosphors 114 for protecting the address electrodes 113.
A plurality of discharge cells are formed with a matrix arrangement structure in the plasma display panel having the configuration described above. Such a discharge cells are formed in the point where the scan electrode or the sustain electrode intersects the address electrode.
FIG. 2 is a diagram illustrating the arrangement of electrodes of a related art plasma display panel.
As shown in FIG. 2, in the related art plasma display panel 200, scan electrodes Y1˜Yn are disposed in parallel with the sustain electrodes Z1·Zn, while address electrodes X1·Xm are disposed to intersect the sacn electrodes Y1˜Yn and the sustain electrodes Z1˜Zn.
A driving apparatus is coupled to the plasma display panel 200 having the configuration described above for applying given driving signals to each of the electrodes. Accordingly, due to the given driving signals by the driving apparatus, an image can be displayed. As described above, the apparatus having a driver coupled to the plasma display panel is called as plasma display apparatus.
Implementing gray scale in a plasma display apparatus having such configuration will be described in FIG. 3.
FIG. 3 illustrates a method for implementing image gradation or gray scale in a related art plasma display apparatus.
As illustrated in FIG. 3, a frame is divided into a plurality of sub-fields having a different number of emission times. Each sub-field is subdivided into a reset period (RPD) for initializing all the cells, an address period (APD) for selecting the cell(s) to be discharged, and a sustain period (SPD) for implementing the gray scale according to the number of discharges. For example, if an image with 256 gradation levels is to be displayed, the frame period (for example, 16.67 ms) corresponding to 1/60 second is divided into eight sub-fields SF1 to SF8, and each of the eight sub-fields SF1 to SF8 are subdivided into a reset period, an address period and a sustain period, as illustrated in FIG. 3.
The reset and address period is the same for every sub-field. The address discharge for selecting a cell to be discharged is performed by the voltage difference between the transparent electrodes that are address electrode X and the scan electrode Y. The sustain period increases by a ratio of 2n (where, n=0, 1, 2, 3, 4, 5, 6, 7) for each sub-field SF1 to SF8. Since the sustain period varies from one sub-field to the next, a specific grey level is achieved by controlling sustain periods, i.e., the number of the sustain discharges.
FIG. 4 illustrates a driving waveform according to a related art method for driving a plasma display panel.
As shown, during a given sub-field, the waveforms associated with the X, Y, and Z electrodes are divided into a reset period for initializing all the cells, an address period for selecting the cells to be discharged, a sustain period for maintaining discharging of the selected cells, and an erase period for eliminating wall charges within each of the discharge cells.
The reset period is further divided into a set-up and set-down period. During the set-up period, a ramp-up waveform (Ramp-up) is applied to all the scan electrodes at the same time. Due to the ramp-up waveform, a dark discharge is occurred within all the discharge cells. This results in wall charges of a positive polarity being built up on the address electrodes X and the sustain electrodes Z, and wall charges of a negative polarity being built up on the scan electrodes Y.
During the set-down period, a ramp-down waveform (Ramp-down), which falls from a positive polarity voltage lower than the peak voltage of the ramp-up waveform to a given voltage lower than a ground level voltage, is applied to all the scan electrode at the same time, causing a weak erase discharge within the cells to sufficiently erase wall charges excessively accumulated in the scan electrodes. Furthermore, the remaining wall charges are uniform inside the cells to the extent that the address discharge can be stably performed.
During the address period, a scan pulse with a negative polarity is applied sequentially to the scan electrodes, and a data pulse with a positive polarity is selectively applied to specific address electrodes in synchronization with the scan pulse. As the voltage difference between the scan pulse and the data pulse is added to the wall voltage generated during the reset period, an address discharge is generated in the cells to which the data pulse is applied. A wall charge is formed inside the selected cells such that when a sustain voltage Vs is applied a discharge occurs. A positive polarity voltage Vz is applied to the sustain electrodes so that erroneous discharge may not occur with the scan electrode by reducing the voltage difference between the sustain electrodes and the scan electrodes during the set-down period and the address period.
During the sustain period, a sustain pulse is alternately applied to the scan electrodes and the sustain electrodes. Every time a sustain pulse is applied, a sustain discharge or display discharge is generated by adding the wall voltage to the sustain pulse voltage in the cells selected during the address period.
Finally, during the erase period, (i.e., after the sustain discharge is completed) an erase ramp waveform (Ramp-ers) having a small pulse width and a low voltage level, is applied to the sustain electrodes to erase the remaining wall charges within all the cells.
Sustain pulses applied during the sustain period in a plasma display apparatus with a related art driving pulse will be described in FIG. 5.
FIG. 5 illustrates a sustain pulse applied during a sustain period in a related art driving waveform.
As shown in FIG. 5, a sustain discharge is occurred by the sustain pulse applied during a sustain period according to a related art driving method. In other words, when a sustain voltage Vs is applied to a scan electrode Y, while a ground voltage level GND is applied to a sustain electrode Z, the sustain discharge is occurred by the scan electrode Y. On the other hand, when a sustain voltage Vs is applied to the sustain electrode Z, while the ground voltage level GND is applied to the scan electrode Y, the sustain discharge is occurred by the sustain electrode Z. Generally, such sustain pulse is alternately applied to the scan electrode Y and the sustain electrode Z.
The sustain pulse described above rises with a given slope during a voltage rising period ER-Up Time, falls with a given slope during a voltage falling period ER-Down Time. The voltage rising period, for example, as shown in FIG. 5, is a period where a voltage rises from the ground voltage level GND to the sustain voltage level. The voltage falling period is a period where a voltage falls from the sustain voltage level to the ground voltage level GND.
A sustain light generated by a sustain pulse of a related art driving pulse will be described in FIG. 6.
FIG. 6 illustrates a sustain light generated by the sustain pulse according to the related art driving method.
As shown in FIG. 6, by the sustain pulse according to the related art driving method, a sustain light is generated in the neighborhood of the time point where the voltage of sustain pulse rises ER-Up Time or where the voltage of sustain pulse reaches a sustain voltage Vs.
The light waveform of the sustain light generated by the sustain pulse according to the related art has a great magnitude and a narrow width, which means that the amount of an instant light is great but the absolute amount of the light is small. Hence, there is a drawback in that the luminance for driving is decreased as the amount of the sustain light generated by one sustain pulse is relatively small.